Enzo needs to hear other opinions other than mine on this, but I am going to go ahead and start with a few thoughts and hope others chime in as well.
I have had Nagel prints damaged coming to me both shipped flat and shipped in a tube.
One person shipped a print flat and did not make sure all the surfaces were the same. They used cut up cardboard boxes with various levels of thickness, bends, and layers. When I opened up the packaging, "Sushi Girl" had been essentially embossed by the areas that were thicker than the others. She had an indentation running vertically down the whole left third of the print.
For Nagel, I would say whether to ship flat or rolled is on a case by case basis. Generally, my experience is that all the larger prints, save "Joan Collins" have shipped rolled just fine in the very wide, 10"-12" diameter tube. If there is any risk, is seems to be that folks do not fill the slack on each end with sufficient bubble wrap or padding to remove any extra space and provide the print's edges cushion should the tube get slammed one way or another. Or they don't put enough padding period.
The other thing is that I would roll the print in Kraft of Glassine tissue that extends beyond the edges, which can be bought in rolls at various art supplies stores and dickblick.com
Glasine is also great for storing your prints. It is designed to be pH neutral and also to block any acidic or base pH from penetrating to reach the protected print. It is almost like wax paper. One thing to be mindful of is do not crinkle it, as it is stiff and could scuff your print's pigment. Just use sheets without crimping in it.. For shipping preparation, I would lay down the 36" wide roll, and put the print down on top of it and have a couple of inches overlap on one end, fold that over, and then roll the print up so it prevents the edge of the print from scratching the pigment on the inside of the roll, and also so there is Glassine extending past the now rolled print on each side so it is slightly protected from being crimped, provided you also pad each side of the tube.
"Joan Collins" is the only Nagel I have that seems like it is almost on illustration board and I would never attempt to roll that print, even in a 12" diameter tube.
For Nagel's smaller, 17" x 25," prints, I think it is best to ship them flat. Jeff Wasserman used heavier weight rag for the hand signed and numbered prints than for the signed in screen, and I would image a print as old as "Mirage Ship" or "Mother Earth's Paris" would risk pigment cracking if rolled.
For this reason, I created a flat shipping folio that I have used many times. When I bid on an auction, I ask the seller if I can ship them the folio to put the print in. They have uniformly been appreciative of this and I have yet to get back a print with any damage from transit this way. (One seller even asked me if he could buy these folios after he got it and put my just won print in it.)
Here are some photos:
I bought double wall cardboard flat sheets from Zepak.
Since most Nagel life time posters are 17" x 25," I made the folio 22" x 30" so the print stored on the side has a couple of inches on each side in case the cardboard gets dinged.
I cut the sheets of cardboard alternate ways, so the fluting would not make it more prone to bending side ways or top to bottom. There are four layers of double wall cardboard, two on each side.
Then for the two innermost sheets closest to the print, I used acid free foam core.
I basically stacked them all together, cut it like a deck of cards, and then started taping up the sides of each half with threaded shipping tape. I ended up with two, three layer thick halves.
I set them side by side, and taped it on the inside, like the spine of a book, and then closed it like a book, and really taped up the outside left side like a book spine. Just to make it clear to sellers, I also used cloth like black tape, so the spine side looks different than the others.
The back on the inside of the folio, I took my roll of glassine, and cut it about 36" x 60,"
folded it in half, and then inserted a 17" x 25" Nagel serigraph, and then folded over the edges
so it locks in the print, then tape down the left, spine side, so the glassine becomes something you just open like two pages of a book, insert the print, close it back and refold over the edges, and you have a very good way to ship and store your smaller prints.
I suppose one could make a super large version of this for Nagel's graphics, but I am personally so fearful of potential bending and the stacking shippers would do, that I would probably go from six layers of cardboard and foam core, to twelve, and then with the 2.5" inches in each side of the print, you're looking at a might big folio to ship.
In my folio, I also added one side of bubble wrap, but this seems like overkill, even to me. I will say, the money I spent making this folio has paid off. I started having prints shipped in this folio about four years ago, and it has yet to have any issues. I do keep adding more packing tape to the outside so the whole thing is all but water tight. The seller simply re-seals the entire edge with packing tape and it is safe and sound.
For my large graphics, I actually ordered at 12" diameter tube from Yazoo Mills and had them directly ship the tube to the seller of my "Seated Man." He is the first of many large prints that have arrived safe and sound. Only one large print has been damaged and it was from the tube being dropped without enough padding, so the print got crimple damage on one end.
One last thing for the moment about packing and shipping prints. As this usually involves touching the prints, I would spend $3.99 and get some cotton gloves designed just for this purpose to put on when you touch your prints.